Hello Jeissa and thanks for bringing such a fun question to the Disney Parks Moms Panel.
I can just imagine how excited all 40 of you must be about arriving at Walt Disney World Resort this coming June to celebrate your darling niece's birthday, what an extra magical time you're sure to have!
In several previous trips to the Magic Kingdom Park I have indeed seen large groups and families having their picture taken in front of
Cinderella Castle by a skilled
Disney PhotoPass Service photographer; so I'm sure with a little added patience to get everyone in the picture looking neat and pretty plus an added sprinkle of pixie dust - you'll be just fine.
To help capture all those wonderful memories you may wish to consider purchasing
Memory Maker for your special trip. A
Memory Maker package enables Guests to download and digitally keep all their Disney PhotoPass Service photos and videos from select Attractions and Character dining plus also includes those super fun
Magic Shots too!
In addition it certainly is possible to schedule an appointment with
Disney Fine Art Photography who will be only too happy to help create a beautiful commemorative family portrait of your magical visit.
If there's anything further I can assist you with, please do pop back to ask me another question.
Have a great Disney day.
~ Jane